With rapid progress of display technologies, a display apparatus with touch function is becoming welcomed by more and more people due to its advantages such as visualized operation and so on. Existing display apparatuses with touch function can typically be classified into on-cell touch panels and in-cell touch panels in terms of different relative positions between the touch panel and the display panel. Compared with the on-cell touch panel, the in-cell panel is thinner and has higher light transmittance.
As for existing display apparatuses, the OLED (Organic Light Emitting Diode) as a current-type light emitting device is applied to the high performance display area more and more due to its advantages such as self luminescence, rapid response, wide angle of view, capability of being fabricated on a flexible substrate, and so on. OLED display apparatus can be classified into a PMOLED (Passive Matrix Driving OLED) type and an AMOLED (Active Matrix Driving OLED) type in terms of different driving manners. Since the AMOLED display has advantages such as low manufacturing cost, high response speed, low power consumption, capability of being used in direct current driving of portable devices, large range of operating temperature and so on, the AMOLED display potentially becomes a new flat display of next generation for replacing the LCD (Liquid Crystal Display). In existing AMOLED display panels, every OLED is driven to emit light by a pixel driving circuit consisting of multiple TFTs (Thin Film Transistors) within one pixel unit on the array substrate to realize display. The pixel driving circuit directly decides the quality of light emitting and displaying of the OLED; therefore, the design of the pixel driving circuit is a key technology of the AMOLED.
It is very hard to achieve consistency of the threshold voltages of TFTs in a large area due to the manufacturing technologies and the material characteristics of TFTs. In the AMOLED display panel, the OLEDs are current sensitive devices and are driven by TFTs to control the light emitting intensity; therefore, if the threshold voltages of the TFTs vary in the display area, the brightness uniformity of the whole picture will be influenced largely, which influences the picture quality.